The present invention relates to a transmission system, in particular, to the transmission system employing a cold standby technique.
Conventionally, transmission systems incorporating two-system transmission-signal processing circuits therein are known, wherein if some abnormality occurs in one transmission-signal processing circuit in operation, the other transmission-signal processing circuit is put into operation as a substitution. Among such transmission systems, some systems employ a cold standby technique that part of one standby-side transmission signal processing circuit holds a non-operation state to save consuming power and/or to elongate the longevity of circuit elements.
For example, as shown in FIG. 1, there is known a system which outputs a signal of approximately 5 Gbps by combining two signals on STM (Synchronous Transfer Mode)-16. This system, which is referred to as SLTE, has a TX shelf (i.e., transmission-signal processing circuit) put into a standby state. The shelf has an OS package including a semiconductor laser (hereinafter referred to as LD) put into an off state.
As is known, in this type of SLTE, each package incorporated in each TX shelf is given the function of outputting an alarm when some failure is caused in the package itself. Using the outputted alarm, a not-shown switching control circuit included within the SLTE switches TX shelves.
Additionally, there are two types of SLTEs which differ from each other in that how a signal (switching trigger) is provided to a switching control circuit to start the switching operation. In other words, in one type of SLTE, the alarm is provided directly to a switching control circuit as a switching trigger, while in the other type of SLTE, the alarm is not a direct switching trigger. Referring to FIGS. 2 and 3, the two types of SLTEs will be described in terms of their constructions and operations.
As can be seen in FIG. 2, a COM shelf belonging to one type of STLE in which the alarm is not directly given, as a switching trigger, to a switching control circuit has a SWCONT package constituting the switching control circuit and an ALMMPU package constituting an alarm monitoring circuit. Each TX shelf has some packages for transmission-signal processing and an ALM IF-TX package not only intervening between the SWCONT package and the ALMMPU package but also operating as described below.
The ALM IF-TX package collects through data bus the alarm outputted in each package, and transfers it to the ALMMPU package. When collecting the alarm. The ALM IF-TX package also determines whether or not a switching trigger is required to be outputted on the basis of the collected alarm as well as the state of the TX shelf itself (i.e., put in operation or not). If the determination is that the output is necessary, the ALM IF-TX package outputs the switching trigger to the SWCONT package. The SWCONT package is configured to send a switching command to both the ALM IF-TX packages when the switching trigger is inputted. In response to the switching command which has been sent from the SWCONT package, the ALM IF-TX packages control a LD of the OS packages connected to them.
On one hand, in the case of the other type of STLE where the alarm is directly given, as a switching trigger, to the switching control circuit, a SWCONT and ALMMPU packages are incorporated in a COM shelf, while an ALM IF-TX package in each TX shelf. Nevertheless, as pictorially shown in FIG. 3, transmission-signal processing packages in each TX shelf and the SWCONT package are connected with each other without being routed to the ALM IF-TX package. As in the SWCONT package, used is a package which concurrently sends an xe2x80x9cLD OFFxe2x80x9d command (switching command) toward the OS package of the TX shelf in operation and an xe2x80x9cLD ONxe2x80x9d command (switching command) toward the OS package of the TX shelf put in a standby state, when the alarm is given from the package of the TX shelf in operation.
However, in the STLE shown in FIG. 2, if any failure occurs in the downstream circuit from the LD of the OS package, switching might be carried out with causes (or positions at which the failures occur) against them unknown.
Besides the switching trigger sent from the ALM IF-TX package, the other switching trigger (hereinafter referred to as FERF signal) resultant from the FERF included in the transmission signal is inputted to the SWCONT package. The FERF signal is generated even if failures occur in the downstream circuit from the LD of the OS package. Additionally, the processing carried out during an interval from the occurrence of any failure to the input of the FERF signal to the SWCONT package needs only an interval of a few microseconds, because the processing is done by hardware. But the alarm detecting processing carried out the ALM IF-TX package depends on a CPU, requiring an intervals of tens of milliseconds.
Thus, where the switching is responsive to the FERE signal resultant from failures caused in the downstream circuits from the LD of the OS package, there is a possibility that the switching (i.e., the LD is off) is completed before the alarm detection processing performed by the ALM IF-TX package. If the switching was completed before that, the alarm relating to the LD output will be issued without an actual failure. (The alarm includes xe2x80x9cOPT OUT DOWNxe2x80x9d from the OS package, and xe2x80x9cOPT IN DOWNxe2x80x9d and xe2x80x9cOPT OUT DOWNxe2x80x9d from a POST AMP package.) Therefore, this situation results in unknown causes to the switching.
In the case of the STLE where the alarm is used as a switching trigger, as shown in FIG. 3, the switching processing and the detection processing are carried out at different speeds in a completely independent manner. Thus, in this case, a situation that the switching has been carried out with unknown cause may arise. Specifically, it is unknown whether the alarm, such as xe2x80x9cOPT OUT DOWNxe2x80x9d from the OS package, truly indicates an actual failure.
The conventional STLE has fear that the switching maybe done with causes unknown.
Furthermore, the conventional SLTE has a problem that the alarm is removed by only reinserting packages whose failure has not been corrected. As described before, in the standby-side TX shelf of which LD is brought into the off state, a few alarms may be issued with no actual failure. Considering this situation, the ALM IF-TX package including a standby-side TX shelf is designed to perform special processing with alarms which have been issued in the off state of the LD placed in the downstream circuits from the LD.
Specifically, as pictorially shown in FIG. 4, the ALM IF-TX package is configured such that it can recognize that the alarm is just information indicating states of corresponding circuits as during an interval from the switching to the exchange of packages (see xe2x80x9cstandby side Ixe2x80x9d in FIG. 4). It is configured that, once another package was reinserted (see xe2x80x9cstandby side IIxe2x80x9d in FIG. 4), the ALM IF-TX package determines that the causes of the alarm have been removed (the package has been exchanged to normal one). Thus, in the conventional STLE, only inserting a package in which some failure is generated leads to the removal of the alarm.
Accordingly, it is a first object of the present invention to provide a cold standby type of transmission system where circuit switching is carried out with known causes.
It is a second object of the present invention to provide a cold standby type of transmission system where erroneously recognizing the states of a package is avoidable.
In order to solve the first object, according to one aspect of the present invention, there is provided a transmission system comprising a first and second transmission-signal processing circuits each of which is configured by combining a plurality of types of packages each having a detecting circuit for detecting an alarm indicative of detection of an failure in each package; a switching control circuit for controlling switching between the first and second transmission-signal processing circuits; a first interface circuit connected with both the first transmission-signal processing circuit and the switching control circuit; and a second interface circuit connected with both the second transmission-signal processing circuit and the switching control circuit. The switching control circuit has an element for receiving a switching trigger signal provided without being routed the first and second interface circuits, the switching trigger corresponding to the alarm, and an element for issuing a switching command toward the first and second interface circuits in response to the reception of the switching trigger signal. And each of the first and second interface circuits has an element for acquiring the alarm output of the detecting circuit of either one of the first and second transmission-signal processing circuits which is connected with either one of the first and second interface circuits in cases where the connected transmission-signal processing circuit is in operation when the switching command is given, the detecting circuit outputting the alarm regardless of generation of the failure if the connected transmission-signal processing circuit is in a standby state, and an element for performing control which makes the connected transmission-signal processing circuit switch into the standby state after the acquisition of the alarm output. In the transmission system thus-configured, in the case that a switching trigger signal different from that sent out based on alarms acquired by the interface circuit is inputted into the switching control circuit, alarms are acquired by the interface circuit prior to circuit switching. Thus, even under a condition that a conventional transmission system might perform its switching with its cause unknown, the transmission system above-configured can do so with its cause known.
It is preferred that each package having the detecting circuit is provided with a holding circuit for holding information corresponding to the alarm even when no power source is supplied to the package, and each of the first and second interface circuits has an element for making the holding circuit hold the alarm output of each paired detecting circuit, an element for performing control which makes the connected transmission-signal processing circuit switch into the standby state after the hold of the alarm output, and an element for determining a condition of each package based on information held by the holding circuit when the connected transmission-signal processing circuit is in the standby state.
According to this preferred configuration, both the first and second objects are accomplished. Furthermore, in order to solve the first object, according to another aspect of the present invention, there is provided a cold standby type of transmission system comprising a first and second transmission-signal processing circuits each of which is configured by combining a plurality of types of packages each having a detecting circuit for detecting an alarm indicative of detection of an failure in each package; a switching control circuit for controlling switching between the first and second transmission-signal processing circuits; a first interface circuit connected with both the first transmission-signal processing circuit and the switching control circuit; and a second interface circuit connected with both the second transmission-signal processing circuit and the switching control circuit. The switching control circuit has an element for receiving the alarm from the package of either one of the first and second transmission-signal processing circuits which is in operation, an element for providing an alarm-detecting command for either one of the first and second transmission-signal processing circuits which is connected with the transmission-signal processing circuit in operation, and an element for performing control which makes the transmission-signal processing circuit in operation switch into a standby state after a given interval starting from providing the alarm-detecting command. And each of the first and second interface circuits has an element for receiving the alarm-detecting command and an element for acquiring the alarm output of each detecting circuit of the plurality of types of packages in either one of the first and second transmission-signal processing circuits which is in operation in response to the alarm-detecting command, the detecting circuit outputting the alarm regardless of generation of the failure if either one of the first and second transmission-signal processing circuits in operation is in the standby state.
In the transmission system thus-configured, when the circuit switching is required, the switching control circuit orders the interface circuit to start acquiring alarms, and waits for a given interval. When the interval terminates, the switching control circuit switches the signal processing circuits between the standby and working sides. Furthermore, even under a condition that a conventional transmission system might perform its switching with its cause unknown, the transmission system above-configured can do so with its cause known.
Preferably, each package having the detecting circuit is provided with a holding circuit for holding information corresponding to the alarm even when no power source is supplied to the package, and each of the first and second interface circuits has an element for making the holding circuit hold the alarm output of each paired detecting circuit.
Therefore, according to this preferred configuration, both the first and second objects are accomplished.